Retainer and method for production thereof

ABSTRACT

A retainer cooperating with a plurality of teeth and configured to stabilize the plurality of teeth, the retainer including at least one elongated arc which is shaped overall adapted to a natural curvature of a lower jaw or an upper jaw, wherein the at least one elongated arc is locally adapted individually to a surface contour of respective abutting teeth, wherein the retainer is machined from a sheet metal plate and includes two mutually parallel surfaces, wherein the sheet metal plate is made from a nickel titanium alloy, preferably a nitinol, wherein the retainer contacts a tooth surface in an installed condition of the retainer, wherein a machined surface of the retainer faces the tooth surface in the installed condition of the retainer, and wherein an upper side or a lower side of the retainer corresponds to an original surface plane of the sheet metal plate.

RELATED APPLICATIONS

This application is a continuation of International applicationPCT/EP2014/054703 filed on Mar. 11, 2014, claiming priority from Germanpatent application DE 10 2013 204 359,7, filed on Mar. 13, 2013 both ofwhich are incorporated in their entirety by this reference.

FIELD OF THE INVENTION

The invention relates to a retainer.

BACKGROUND OF THE INVENTION

Retainers have already been known for some time. They basically serve tofix the tooth position of a patient. That is, by means of a retainer astatus quo is fixed with respect to the tooth position in order toprevent possible changes in the tooth position over time.

Particularly typical is the use of retainers in the course of apost-treatment of an orthodontic treatment. The latter involved anactive influence on the tooth position of a patient, wherein by means ofsuitable devices forces are exerted to the teeth, such that they changetheir position or orientation over time. After such an orthodontictreatment is finished and the use of the respective device is completedthe teeth tend to return to their former position. If no post-treatmentis performed the result obtained by means of the active treatment willat least partially regress and consequently negate the active treatment.

Therefore, subsequently to the active treatment typically the use of aretainer is recommended which fixes the newly obtained tooth position.In order to achieve this, such retainers are connected to a plurality ofteeth, wherein the retainer is adapted to receive forces produced due toa desired intrinsic mobility of a tooth and to distribute the forces tothe remaining teeth. Thus, a movement of the tooth is prevented. Suchretainers are known for example from DE 20 2012 004 419 U1 and DE 102 45008 A1, wherein in the latter document a so-called “2-point retainer” isdescribed, which is firmly connected with only two teeth.

In the known retainers it has proven to be particularly disadvantageousthat a precise adaption of the respective retainer to the individualcontours of the teeth to be fixed on the one hand is very expensive andon the other hand is usually characterized by only low precision even inthe case of careful handling by an experienced dental technician. Thisis mainly due to the production of today's known retainers, which areadapted to the shape of the respective dental impression in a manualprocess by bending a starting material—typically a metal strand. Theprecision of such a processing is naturally limited, wherein thefinished retainer can have a distance in the order of a few millimetersfrom a tooth to be fixed. Then, in order to close this “gap” betweenretainer and tooth it is necessary to provide a correspondingly largeradhesive bond that reliably encloses the retainers despite of its greatdistance from the tooth and consequently connects the retainer to theteeth in a force-fitting manner. This is disadvantageous both for thewearing comfort of the retainer and its durability, because shear forcesoccur during chewing and acting on the retainer or its adhesive bond arethe greater the more “attack surface” they provide in the oral cavity.This often results in that a retainer is detached locally and then hasto be fixed again manually. Likewise, regularly a fracture of theretainer occurs.

Furthermore, the known retainers have the disadvantage that their purelypassive effect can already be “activated” by minor accidentaldislocations of the retainer. Thus, it regularly happens that a retainerin an interdental area, where it freely, that is unglued, extends fromone tooth to the respective adjacent tooth, is accidentally bent, forexample as a result of an interacting chewing force.

By bending the projected length of the retainer is locally reduced,which results in that the retainer from then on pulls the adjacent teethto one another. That is, the retainer is changed by means of theunwanted deformation from a passive to an active element, which now nolonger acts as a purely fixing element, but actively influences thetooth position. Such an influence, however, has to be avoided in anycase, since the active dental treatment is typically already completedat the time of use of the retainer and further teeth movements are notdesirable. If a deformation of a retainer occurs, it may even benecessary to completely replace it.

Another disadvantage of today's retainers is their fixing effect, whichcan be referred to as “interlocking”. This interlocking means that aretainer known in the art in fact achieves the desired stabilizingeffect, however, it couples the teeth so strongly to each other, thatany load acting locally on a tooth is substantially evenly distributedto all teeth. An independent movement in a sagittal direction is largelysuppressed because of the retainer. The same applies to verticalmovements and rotations of the teeth about their vertical axis. As aconsequence the force impact due to external forces is decreasedpermanently for each individual tooth which has the consequence that thealveolar bone in which the teeth are anchored by their roots, is muchless irritated than is the case without the retainer, i.e. under“natural conditions”. This irritation, however, is particularlyimportant because it leads to a stimulation of the bone tissue, so thatit will be preserved. If the irritation of the bone tissue is decreased,it degenerates. The decreasing force impact on each individual tooth hasaccordingly the consequence that the alveolar bone degenerates in theregion of the “interlocked” teeth because the impact of external forceson the bone tissue locally decreases.

From the foregoing it is clear that two kinds of tooth movements have tobe distinguished: on the one hand tooth migrations occur, whichrepresent a continuous movement of the tooth back to a malposition,wherein said tooth migrations should be suppressed by the retainer. Onthe other hand teeth also have a certain intrinsic mobility due to whichthe teeth are movable in all directions within a certain margin (about0.2 mm) in particular when chewing loads occur, wherein the teeth returnto their initial position after the load is relieved. However, theseintrinsic movements are extremely important because of the associatedstimulation of the bone tissue and should be restricted as little aspossible by a retainer.

From EP 1782748 A1 a retainer is known which is made from of a zirconiumoxide, i.e. a ceramic material. Due to the fact that the zirconium oxideis not deformable the retainer is milled or ground from a block.Zirconium oxide is characterized by a high flexural strength and istherefore very rigid and unyielding. However, because of the risk offracture inherent to the brittle ceramic material the known retainer isvery thick-walled and voluminous. However, these characteristics of theknown retainers result in the above-described disadvantage of“interlocking”, which restricts the movement of the teeth in the socket(tooth socket) and become non-physiological, which eventually leads to adegeneration of the bone tissue.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the drawbacks ofthe known retainers.

The object is achieved by a retainer cooperating with a plurality ofteeth and suitable for stabilizing the teeth, including at least oneelongated arc, wherein the arc locally comprises a curved shapefollowing the natural curvature of a lower jaw or an upper jaw and islocally individually adapted to a surface contour of a respectiveabutting tooth, wherein the retainer is made of a metal and is machinedfrom a plate-shaped part, in particular a sheet, of the metal whichcomprises two mutually parallel surfaces.

Furthermore, the object is achieved by a method of manufacturing anabove-mentioned retainer, the method including the steps:

a) a contour of teeth individually to be stabilized is detected.

b) the retainer is machined from a metal sheet.

Herein, the term “contour” of the teeth quasi means their topography.This means that the detection of the contour of the teeth includes thedetection of the tooth surface which is to cooperate with the retainersuch that the treating physician is provided with information indicatingwhich shape the retainer should have both globally and locally in orderto abut the teeth as closely as possible.

With respect to the retainer described above the aforementioned objectis achieved according to the invention in that the metal is formed froma nickel titanium alloy, more preferably from a nitinol and a machinedsurface of the retainer in its installed state faces a tooth surfacewhich the retainer abuts, and an upper surface or a lower surface of theretainer corresponds to an original metal sheet plane. Nickel titaniumalloys and nitinol are shape memory materials that are particularly wellsuited for the retainer according to the invention, since they have aso-called “pseudo-elastic” material behavior (also called “superelasticity”). This material behavior means with respect to the presentinvention that the retainer can even experience relatively largedeflections without thereby being deformed plastically—i.e. permanently.The elastic region of the shape memory material is formed unusuallylarge due to a phase transformation within the material under theinfluence of tension and can exceed twenty times the elastic region of a“normal” steel, such as is commonly used for today's retainers. Thisleads to the particular advantage that such a retainer according to theinvention practically cannot be deformed plastically, which means that a“kink” or another accidental permanent deformation of the retainer isnot possible. Thus, it is not possible that the retainer according tothe invention is accidentally “activated” due to a local deflection of asingle tooth as a result of its intrinsic mobility (for example underthe impact of high local chewing forces caused e.g. by biting on agrain). As a result a movement of the teeth caused by the retainercomparable to an orthodontic treatment is excluded with the use of theretainer according to the invention.

Furthermore, the shape memory material is advantageous in terms of theabove-described problems with respect to the lacking stimulation of thealveolar bone. This is because short-term positional changes of theteeth, which are based on local forces acting on individual teeth—i.e.as a part of their intrinsic mobility—are enabled due to thepseudo-elasticity of the material, i.e. extremely low elastic restoringforces. By means of a reversible, elastic deformation of the retainerthe applied force is yielded and the tooth can be deflected in a naturalamount within the socket, that is in the tooth socket, where the toothis suspended by collagen fibers. Once the force impact is no longerpresent, both the retainer and the affected tooth return to theiroriginal shape or position.

The pseudo elasticity of the shape memory material, moreover, promotesthe durability of the retainer according to the invention. Thus, it isnot subject to the risk of a deformation induced fracture or a “fatigue”of the restoring properties.

In addition, the shape memory material is relatively soft due to the lowmodulus of elasticity, so that it can be easier deformed elastically.Thus, a breakage of a junction to a tooth is less likely to occur thanwith retainers of the prior art. Furthermore, the low stiffness ispositive in view of the possibility of a sagittal and verticaldeformation of the individual teeth, since the retainer couples orinterlocks the connected teeth less stiffly.

Accordingly, a retainer formed from a shape memory material is alsopreferable with respect to a lower interlocking effect.

Through the use of nickel titanium alloys, in particular nitinol, apreviously existing conflict of interest in the use and formation ofretainers is solved: on the one hand, one strives to connect the teethto one another in a force transmitting manner in order to counteractunwanted tooth movements and tooth migrations. On the other hand thephysiological intrinsic mobility of the individual teeth should berestricted as little as possible. Both are possible with the method orthe retainer according to the invention, however, not with the retainerspreviously known. This is the case, because nickel titanium alloys, inparticular nitinol, are characterized in that with rapidly occurringloads an (elastic) deformation can take place and with slowly occurringloads no deformation of the retainer is caused. This is particularlyadvantageous because in chewing movements the desired shortly occurringmovements of the teeth are permitted in the frame of their intrinsicmobility while continuous movements of the teeth or tooth migrationtowards a malposition are being suppressed. Even if deflections arepermitted, there is always a small restoring force towards the initialposition of the retainer. Steel, for example, has a certain restoringforce, but this is significantly lower and there is a high probabilitythat the steel will be permanently bent and thus will exert no restoringforce at all, but on the contrary exerts a force on the teeth, whichdirects them into a malposition.

Regarding the feature of the retainer according to the invention that amachined surface of the retainer in its installed state faces a toothsurface which the retainer abuts and an upper surface or a lower surfaceof the retainer corresponds to the original plane of the metal sheet,this is advantageous because in this way a bending free separation ofthe retainer is possible or takes place. This means that the retainer isproduced in the form in which it eventually abuts the teeth of apatient. A bending of the metal sheet for producing the retainer is notpossible at all for a material with super elastic properties, because nopermanent deformations can be made. The retainer according to theinvention thus is a finished product that can be used without furtherprocessing. An advantageous finishing process in the form ofelectro-polishing is not considered at this point.

In a retainer according to the invention, which is connected in bondingportions by means of a bonding material to the respective adjacent teethin a force-transmitting manner, and preferably is embedded in a bondingmaterial adherent to the respective tooth, it is also particularlyadvantageous when in each of the bonding portions a maximum distancebetween a respective tooth surface and a position of the retainer, whichmeasured perpendicular to the respective tooth surface has the smallestdistance to this tooth surface, is at most 0.1 mm, preferably at most0.01 mm, more preferably at most 0.005 mm. Such a retainer is adaptedparticularly precisely to the natural contour of the respective teeth.This is advantageous in that the insertion of such a retainer isparticularly easy for the treating specialist, since the retainerpractically exactly abuts the teeth only in a single position.Therefore, an accidental “oblique” installation is almost impossible. Inaddition, the exact adaptation in accordance with the above explanationpromotes the use of thin bonding portions, which in turn has a positiveeffect on the durability and susceptibility to failures of the retainer.Moreover, a thin layer of the bonding material is perceived as lessdisturbing by the patient.

Advantageously, the retainer is locally formed so as to protrude atleast partially into at least one interdental space between two adjacentteeth so that a relative motion between the retainer and the teeth in alongitudinal direction of the retainer is blocked even if the retainerabuts the teeth in an unconnected state.

Here, the term “unconnected state” means that the retainer is not yetconnected to the teeth in a force-transferring manner and consequently,for example, could be manually removed from the oral cavity again. Onthe contrary, in a “connected state” the retainer is connected fixedlywith the teeth, in particular bonded. The described shaping of theretainer is exclusively possible by means of the method according to theinvention. A formation of regions that protrude into the interdentalspaces is inconceivable by means of the usual prior art deformationmethods.

The shaping of the retainer in the manner described provides a number ofadvantages. For this purpose, reference is made to the above-describedproblem of “interlocking”. This arises from the fact that today's usualretainers couple the teeth strongly to each other, so that anindependent intrinsic motion of the teeth is restricted very strongly.The accompanying problem of a degeneration of the alveolar bone hasalready been described above. Through the guidance of the retainer upinto the interdental spaces now the effect is achieved, that theso-called “free length”, that is the length over which the retainerabuts freely, i.e. “unbonded” at the teeth between two adjacent teeth,is considerably greater in the retainer according to the invention thanin known retainers. In the latter, the retainer extends essentiallystraight between two adjacent junctions, i.e. over the shortest possiblepath. In the retainer according to the invention, however, the retainerextends in a kind of “detour” as the retainer is guided up into theinterdental spaces. This has the consequence that a “built-in length” ofthe retainer according to the invention, i.e. an unwound length thereof,is significantly longer than the unwound length of a conventionalretainer. Here again the pseudo-elastic behavior of the nickel-titaniumalloy or the nitinol comes into effect, because only if a pseudo-elasticmaterial is used a noticeable increase in the deflection ability can beachieved due to an increase of the per se short distance between twoteeth. By means of the increased length between two adhesive bonds theflexibility of the retainer is further increased. If, however, a rigidmaterial such as ceramic is used for a retainer, this may indeed also bedesigned such that it protrudes into the interdental spaces of adjacentteeth, however, the flexibility or elasticity of the retainer is notincreased, but rather due to the rigidity of the ceramic material stillno sufficient intrinsic movements of the teeth are enabled.

The increased free length between two junctions eventually has theadvantageous effect of reducing the described interlocking of the teethas compared to what is known in the art. This is due to the fact thatthe coupling of a respective tooth to the respective adjacent tooth isthe less the longer the bonding portion is, which couples both teeth toeach other. This greater freedom of movement manifests itself inpractice in that the individual teeth can move significantly more freelyboth in the sagittal and in the transverse and vertical directions whenusing the retainer according to the invention clearly than in use of aconventional retainer. In addition, the tooth is able to rotate and tochange its axial inclination. Thus, the previously disadvantageous lackof a stimulation of the alveolar bone is substantially eliminated.Nevertheless, the coupling effect of the teeth in the transversedirection, i.e. the coupling, which in principle is to be achieved bymeans of the retainer, is not adversely affected by the greater freelength of the retainer according to the invention.

The greater free length of the retainer according to the invention isalso advantageous for its durability. Thus, in the retainer according tothe invention fractures of the arc or the respective junction occurrelative rarely. This is because the arc can be more easily deformedfreely than in retainers according to the prior art. In the latterdeformations have to be reduced over short distances, wherein thedeflections sometimes result in a fracture of the retainer or a fractureof the adjacent junction.

Furthermore, the high accuracy of fit which is demonstrated here by theadaptation of the retainer up into the interdental spaces, is basicallyadvantageous for the wearing comfort of the retainer. Here, reference ismade to the above statements.

In an advantageous embodiment of the retainer the arc has locally aradius of curvature of 1.0 mm or less, preferably 0.5 mm or less, morepreferably 0.2 mm or less. Such a small radius of curvature is providedfor example in the region of an interdental space. At such a point thearc of the retainer extends locally quasi towards a “tip”. In addition,such “sharp” curvatures in the arc may be adapted to locally replicatetopographies present at the tooth surfaces. A formation of such bendingradii is inconceivable with conventional retainers.

The retainer according to the invention is particularly advantageouswhen the arc comprises a parallelogram shaped, preferably a square crosssection, wherein the side lengths of the cross section are at most 0.7mm, preferably at most 0.5 mm, more preferably at most 0.3 mm. A squarecross section is particularly suitable. An “edge-shaped” configurationof the retainer primarily offers the advantage of a so-called “torquecontrol”, i.e. of stabilizing the inclination or the axial inclinationof the teeth. This is due to the fact that the edge-shaped retainer canappropriately interlock with the bonding material of the junction andthus prevents it from the respective rotational movement. Usualretainers on the other hand have a round or oval cross section, by meansof which such a stabilization due to lack of interlocking of the crosssection of the retainer with the respective adhesive bond is notobtained.

The small cross sectional size of the retainer according to theinvention moreover results in that the junctions with the tooth surfacecan be made relative shallow. This on the one hand promotes thedurability of the retainer because an attack surface for shear forcescan be minimized and on the other hand the wearing comfort since thepatient only feels a little unevenness on the tooth surfaces.

Preferably, the retainer according to the invention is used as aso-called “6-point retainer” and as such is connected to more than twoteeth or more than three teeth in a force-transmitting manner. However,a use as a so-called “2-point retainer” is conceivable in principle.

With regard to the connection of the retainer to the teeth it isparticularly advantageous if the retainer is fully enclosed by thebonding material at the bonding portions. This means that the retaineris surrounded by the bonding material at the bonding portions at foursides. Thus, the retainer is at least in portions completely embeddedwithin the plastic mass, so that in the corresponding portion no part ofthe retainer is exposed or visible. In this way, a particularlypermanent connection between the retainer and the tooth is provided.

In a particularly advantageous embodiment the retainer is made in onepiece. This is the normal case in use of the method according to theinvention, because in the course of preparing the retainer from themetal sheet a single continuous piece is obtained, which forms thecomplete retainer. Nevertheless, it is conceivable to assemble theretainer according to the invention from a plurality of individualparts.

If one regards the retainer according to the invention as enclosed by afictive inner enveloping parabola and a fictive outer envelopingparabola seen in the plan view, wherein the inner enveloping parabolaabuts the innermost points of the retainer and the outer envelopingparabola abuts the outermost points of the retainer, then such aretainer is preferable, in which locally in the region of an interdentalspace a maximum distance between the inner enveloping parabola and theouter enveloping parabola measured perpendicular to the inner envelopingparabola is at least 1.0 mm, preferably 1.5 mm, more preferably 2.0 mm.This distance between the enveloping parabolas is conceivable as ameasure of the “penetration depth” of the retainer into the interdentalspaces. The further the retainer follows these interdental spaces, themore precisely it rests on the teeth and the longer is the free lengthbetween adjacent junctions. In this regard, a retainer comprising thedistances described is particularly advantageous.

Further, it may be advantageous when the retainer at least partially hasa roughened surface, wherein preferably all surfaces (lower surface,upper surface, front surface, back surface) of the retainer areroughened. Such roughening enables a better bond between the retainerand the material by means of which the retainer is connected to theteeth.

In an advantageous embodiment the retainer is treated byelectro-polishing or plasma polishing. The advantages of such retainershave already been explained above.

Finally, it is particularly advantageous if the nickel titanium alloyhas an AF temperature between 25° C. and 35° C., preferably between 27°C. and 33° C., more preferably between 29° C. and 31° C. It has beenfound that the closer the AF temperature is at the temperature at whichthe workpiece is used, which in the case of retainers corresponds to thebody temperature of about 37° C. the more reliable the desired region ofthe stress-induced martensite plateau is reached in elongation of thematerial.

According to the invention the underlying object is achieved startingfrom a method of the type described above by the following method steps:

c) the detected contour of the teeth is converted in a preferablydigital model and the retainer is designed on the basis of the model.

d) the designed retainer is machined from the metal sheet, which is madefrom of a nickel titanium alloy, preferably of nitinol, on the basis ofthe model by means of a computer-controlled process, wherein a machiningsurface of the retainer in its installed state faces to a tooth surfacewhich the retainer abuts, and an upper surface or a lower surface of theretainer corresponds to an original metal sheet plane.

The invention is based on the idea that an improvement of the precisionin the adaptation of the retainer to the respective teeth contours ofthe patient results in a considerable improvement of both the effect ofthe retainer and the wearing comfort. Furthermore, accidental treatmenterrors that are based on an accidental activation of a retainer, can beavoided.

The method according to the invention enables a significant increase inthe precision of the finished retainer over known today's retainers in away that locally a distance of the retainer from the respective toothsurface, which it is to abut, is very low. From the detected contour aparticularly precise model for a retainer can be obtained by the use ofa computer with a corresponding CAD (Computer Aided Design) software.Based on this model by means of a computer-controlled machining process(Computer Aided Manufacturing—CAM) finally the retainer can be workedout automatically from the metal sheet in the exact shape specified bythe CAD model. This procedure is therefore also referred to as “CAD-CAMmethod”. Since the retainer according to the invention is worked outfrom the metal sheet, this method is a so-called subtractive method.

As a result, the method according to the invention produces a retainerwhich exactly abuts the contour of the detected teeth and has a securefit. In particular, a subsequent deformation or processing of theretainer—whether by machine or by hand—is not necessary and, when usinga nickel titanium alloy, in particular nitinol, with its pseudo-elasticproperties, even impossible, because the material after an imposeddeformation returns into its initial position. The retainer according tothe invention, thus, once it has been worked out from the metal sheet,obtains directly its eventual shape (both globally and locally), whereinno further adaptations are necessary or possible. This results inseveral advantages:

The junctions at which the retainer is to be connected to the respectivetooth, can be implemented much shallower than is the case according tothe prior art. That is, a layer thickness of the required plasticmaterial which forms the junction, is smaller.

This is due to the fact that the retainer abuts very closely or directlyat the corresponding tooth surface. The plastic layer, by means of whichsuch retainers are typically connected to the teeth, is required to havea comparatively small extension in a direction perpendicular to thetooth surface in order to fully enclose or embed or encase the retainer.A bridging of free spaces between the retainer and the tooth, as isregularly required in the prior art, is not necessary. A “shallow”junction on the one hand considerably improves the wearing comfort ofsuch a retainer. This primarily concerns a more pleasant wearingcomfort, since the spatial extension of the foreign body, which theretainer with the bonding material ultimately represents in thepatient's mouth, is very small. In addition, it facilitates thepatient's oral hygiene. On the other hand a thin junction due to itssmall dimensions within the oral cavity has a significantly smallersurface than is the case with junctions according to the prior art, andis therefore subjected to significantly lower shear forces or chewingforces. The latter is particularly advantageous for the durability of aretainer produced by means of the method according to the invention,since the probability of detachment of the retainer from one or moreteeth due to such force impacts is significantly reduced. In view of thedurability of the retainer it is also advantageous that by means of thepseudo elasticity of the nickel titanium alloy or the nitinol at a forceimpact by mastication and a resultant tooth deflection less stress, i.e.tension, is produced in the retainer tooth composite, which in the worstcase could lead to stress fracture.

The lack of plastic deformability of a retainer formed from a shapememory material is also the reason why such retainers are not yetavailable on the market. Thus, the currently known production processes,which—as described—require an individual molding of the retainer withrespect to the respective row of teeth to be fixed by bending, are notadapted or cannot be used to form such a retainer from a nickel titaniumalloy, because it cannot be deformed permanently or plastically. Only bymeans of the method according to the invention—i.e. by working out theretainer from a metal sheet in accordance with the specifiedorientation—the use of a shape memory material is conceivable at all.

Another important advantage of a precisely shaped retainer is itssimplicity in terms of its application or introduction in a patient. Inretainers according to the prior art, the treating physician is quicklytempted to apply points of the retainer, at which a distance between thesame and the tooth to be fixed is relatively large, manually andsubsequently to bond. During this application the retainer iselastically deformed and accordingly develops to a restoring force,which tends to move it back into its previous position. By fixing theretainer to the tooth this restoring force is preserved and acts fromnow on onto the respective tooth. This means that the retainer acts nolonger as a purely passive element which merely fixes the teeth in theircurrent position, but is activated and causes a movement of therespective tooth because of the force. By means of the productionprocess of the invention the retainer is, however, precisely adapted tothe teeth such that such an accidental activation of the same is almostimpossible and in particular not necessary. Consequently, by the methodthe later success of treatment can be significantly improved and the useof a retainer is significantly safer than in the prior art.

The retainer is worked out from the metal sheet in such a way, that amachining surface of the retainer in an installed state thereof faces toa tooth surface at which the retainer abuts and which is adapted to therespective surface contours of the respective teeth and an upper surfaceor a lower surface of the retainer corresponds to an original metalsheet plane. An “upper surface” and a “lower surface” of the retainermean those surfaces thereof that are aligned parallel to one another. Inthe example of FIG. 1 of the exemplary embodiments the upper surface ofthe retainer is the surface that is visible to the viewer of the figure.The “machining surface” means the surface of the retainer, which isobtained through working out the retainer from the metal sheet. Thus,the machining surface is that plane, which is arranged perpendicular tothe plane of FIG. 1 of the exemplary embodiments. The machining surfacetypically abuts the surface of the respective teeth to be fixed. Thismachining surface at least partially abuts the tooth surface. Theopposite plane facing away from the tooth surface can equally beinterpreted as a machining surface.

This orientation during working out the retainer from the metal sheetenables to produce the same directly in the shape in which it will laterbe applied to the teeth of the respective patient. In particular, thecurved path which globally viewed is approximately parabolic, can be“traversed” directly automated by means of an appropriate tool, so thatthe retainer can be separated without bending or deformation of thematerial. From the above mentioned DE 102 45 008 A1 basically also amethod for working out a retainer from a metal sheet can be extracted,wherein reference is made to the exemplary embodiment according to FIG.4 of said document. However, in the retainer described therein themachining surface also called as processing plane coincides with theupper surface and the lower surface, respectively, of the retainer. Theworked out retainer therefore as a result is “flat” (which due to thesignificantly increased adhesive end portions is required) and has to beadapted in a further step to the teeth, wherein it is typically bent.Such an additional step, which is typically carried out manually, inturn carries the risk of inaccuracy regarding the fit of the retainerand is not necessary by means of the method according to the inventionand due to the characteristics of the nickel titanium alloy even notpossible.

The method according to the invention is particularly advantageous ifthe retainer is cut out from the metal sheet by laser cutting or by wireerosion, wherein by use of this method the cutting out is carried out bythe impact of heat and not by a shearing process of two cutting edgesmoving past each other. Such cutting methods are particularly accurate.Furthermore, associated devices which are adapted for cutting metalsheets in an automated manner are readily available. Alternatively,however, other methods are conceivable, for example, water-jet cutting.

The method is also particularly advantageous if the contour of the teethto be stabilized is detected intraorally. This is enabled by means ofso-called “intraoral scanners”. In the meantime, conventional mouldingprocesses, in which an impression (negative) of the teeth be stabilizedis made by means of an impression material and a positive is obtained bycasting the impression with a plaster material, are of particular highquality. Nevertheless, the precision of intraoral scans is betterprocess related, since even when using good impression materials alwaysa drying-induced shrinkage takes place and during the transfer of thecontour information of the natural tooth to the impression template andin turn from the template to the finished form inevitably a loss occurs.In addition, regularly bubbles by entrapped air occur during theimpression process which has a negative effect on the precision of thepositive. In today's usual retainers this is irrelevant since theirprecision cannot detect such small discrepancies between the model andthe real tooth. In retainers which are produced by means of the methodaccording to the invention the intraoral scan, however, can provide anadvantage in the final result of the retainer.

In a particularly advantageous embodiment of the method according to theinvention the metal sheet from which the retainer is worked out, is madeup of a pre-curved metal sheet, wherein a curvature axis about which themetal sheet is at least curved in an unbent state of the metal sheetextends in a metal sheet plane. A pre-curved metal sheet during theproduction process offers the opportunity to produce the retainerslikewise curved.

By use of a plane metal sheet the retainer produced according to theinvention has an arc shape, wherein the retainer, however, has twoplanes extending parallel to each other. Consequently, the retainerworked out from a plan metal sheet could be laid flat on a planesurface, such as a tabletop, wherein a lower surface of the retainerwould form a full-surface contact with the tabletop. By means of the useof pre-curved metal sheets from which the retainer is worked out, theretainer obtains an additional (vertical) dimension, because as aconsequence it also has a curved geometry. Using the example of thetabletop this would mean that the retainer would only rest on the planetabletop with its lower surface in portions and otherwise would beraised from the tabletop. Such an option to form the retainer with anadditional dimension possibly allows a better adaptation of the retainerto the global shape of the dental arc.

In a particularly advantageous method the retainer is electro-polishedor plasma polished after it has been cut out from the sheet, wherebyedges are rounded. Such a treatment of the retainer reduces themicro-roughness and the nano-roughness of its surface and thus impedessticking of potentially harmful germs. Further, the corrosion resistanceof the retainer is increased. The upper surface and the lower surfacenewly formed after polishing according to the present invention arelikewise to be understood as an “original metal sheet plane” accordingto the independent method claim, since the removal of the material bypolishing is only small, in particular since the removal of materialoccurs in the micrometer range.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, the invention described above is explained in detail withreference to an exemplary embodiment illustrated in drawing figures,wherein:

FIG. 1 is a plan view of a retainer according to the invention for usein the upper jaw;

FIG. 2 is similar to FIG. 1, but is used on a model of the upper jaw;

FIG. 3 is a sketch of a retainer used on a model of a lower jaw:

FIG. 4 is similar to FIG. 1, but is illustrated as a three-dimensionallattice model;

FIG. 5 is a cross section through a teeth provided with a retaineraccording to the invention;

FIG. 6 is an enlarged view of the retainer of FIG. 5;

FIG. 6a is an enlarged view of an alternatively formed retainer; and

FIG. 7 is a plan view of a nitinol sheet with a worked out retainer.

DETAILED DESCRIPTION OF THE INVENTION

A first exemplary embodiment, shown in FIG. 1, includes a retainer 1,which is adapted for use in a upper jaw. The retainer 1 is configured asa 6-point retainer and is connected to six teeth in a force-transmittingmanner after it has been inserted into the respective patient. Theretainer 1 is shown in FIG. 1 in a plan view, so that an upper surface 2of the retainer 1 is visible.

The retainer 1 includes an arc 3, the global shape of which isparabolic. This global shape of the arc 3 is determined by the shape ofthe respective upper jaw, into which the retainer 1 is to be inserted.The arc 3 includes locally individual formations 4, which can be dividedinto two categories. The first category refers to formations 4 in theform of “shallow waves” 5 which are configured to adapt the retainer 1to an individual topography of the adjacent teeth. These shallow waves 5are therefore correspondingly adapted to an individual tooth shape of apatient. The second category describes “tips” 6 which form the points ofthe arc 3, which enter into interdental spaces between adjacent teeth.In the tips 6 the arc 3 has small radii of curvature, which are here inthe range of 0.5 mm to 1.0 mm. These tips 6 are different from the waves5 by means of their amplitudes relative to the global shape of the arc3.

This can be shown on the basis of two enveloping parabolas 7, 8enclosing the arc 3 and shown in dashed lines in FIG. 1. Theseenveloping parabolas 7, 8 describe an inner boundary line and an outerboundary line of the retainer 1, wherein the inner enveloping parabola 7includes those points that are located innermost relative to the shapeof the retainer 1 and the outer enveloping parabola includes thosepoints that are located outermost relative to the shape of the retainer1. Thus, the outer enveloping parabola 8 extends substantially throughmaximum points of the tips 6. In the example shown a distance asmeasured perpendicular to the enveloping parabola 7 between the same andthe outer enveloping parabola 8 is continuously about 2 mm. This valuedescribes at the same time the above-mentioned amplitude of the tips 6.A parabola which would be laid substantially through maximum points ofthe shallow waves 5 would have a much smaller distance from the innerenveloping parabola 7. That is, the amplitude of the waves 5 incomparison to the tips 6 is small. This is clearly visible in the formof the retainer 1 shown.

The retainer 1 is formed from the material nitinol and was cut out froma corresponding nitinol sheet by a laser cutting process. Prior to thisstep it is always necessary to detect the respective contour to bereproduced of teeth to be stabilized. This is typically implemented bythe scan of an impression that reproduces a dental impression of theupper jaw or lower jaw, or by means of a so-called “intraoral scan”which is made by means of an intraoral scanner. In the latter method,the shape of the teeth is detected directly in the patient's mouth.Here, it is advantageous that this method is possible comparativelyquickly and allows greater precision than an impression process.

The result of the respective scan of the teeth is then processed bymeans of a CAD software and a three-dimensional model of the retainer 1is created, which is adapted very well to the scan and consequently tothe real topography of the respective teeth. Based on the modelsubsequently the laser is programmed, by means of which the retainer 1is cut out. This process step is also referred to as computer aidedmanufacturing (CAM).

The retainer 1 is shown in FIG. 2 in an inserted state in which theretainer 1 is initially loosely applied to the teeth. The retainer 1 isformed such that a distance between a tooth surface at which theretainer 1 abuts and a point of the retainer 1, the distance of whichmeasured perpendicular to the tooth surface is the smallest, is at most10 μm. i.e. 0.01 mm. Such a precision cannot be realized with retainersaccording to the prior art. The resulting advantages are explained indetail above.

FIG. 3 shows another example of a retainer 1′ according to theinvention, wherein the retainer 1′ is adapted for use in a lower jaw.The retainer 1′ like the retainer 1 is connected to six teeth in aforce-transmitting manner, however, the retainer is shown in FIG. 3 inits inserted state, i.e. without the junctions necessary for aconnection. Here, tips 6′ of the retainer 1′ protrude into interdentalspaces between the teeth such that shifting the retainer 1′ relative tothe teeth is blocked at least in a transverse direction. From the figureit is clear that the amplitude of the tips 6′ are significantly largerin the retainer 1′ than is the case in the retainer 1. This results fromthe natural shape of the teeth.

The retainer 1 is finally shown in FIG. 4 in a three-dimensional latticemodel. From the illustration it is clear that the retainer 1 has asquare cross-section, wherein a side length of the cross section is 0.3mm. Likewise, in FIG. 4 both a front surface 9 and a rear surface 10 ofthe retainer 1 are shown. These are arranged parallel to one another,wherein the front surface 9 faces a tooth surface of the respectiveabutting tooth in an installed state of the retainer 1. Perpendicular tothe front surface 9 and the rear surface 10 the upper surface 2 and alower surface 11 of the retainer 1 are oriented.

The upper surface 2 and the lower surface 11 of the retainer 1 eachextend in one plane. These planes define a metal sheet (not shown) fromwhich the retainer 1 was originally machined, wherein the metal sheethas a thickness of 0.3 mm. This means that a machining tool (laser,water jet, erosion wire, etc.) has been traversed parallel to the uppersurface 2 of the retainer 1 over the metal sheet corresponding to thecontour of the retainer 1 in order to machine the retainer 1 from themetal sheet. By means of this process step the front surface 9 and theback surface 10 of the retainer 1 have been obtained. These aretherefore to be understood as processing planes 12 or machining surfaces13 because they represent the planes that have been processed or wherethe retainer 1 has been machined. After machining the retainer 1 isprovided directly in the illustrated form and may be applied to thepatient's teeth without further adaptations.

FIG. 5 shows a cross section through an incisor 14 which is providedwith the retainer 1 according to the invention of FIG. 1, wherein onlythe area of the incisor 14 is shown, which is located above the gums 15.For the sake of clarity, FIG. 6 shows an enlarged view of the retainer 1in FIG. 5. In a bonding portion—in which the retainer 1 is bonded withthe incisor 14—the retainer 1 is embedded into a bonding material 16,which previously has been applied onto an inner tooth surface 17 andabuts quasi directly the tooth surface 17. The surface with which theretainer 1 abuts the tooth surface 17 corresponds to the machiningsurface 13 of the retainer 1, i.e. a cutting edge 18 which was formedduring the production of the retainer 1. The upper surface 2 of theretainer 1 corresponds to an upper metal sheet surface 19 and the lowersurface 11 of the retainer 1 corresponds to a lower metal sheet surface,wherein said upper and lower sheet surface 19 are parallel to eachother. The upper and the lower sheet surface correspond to an originalmetal sheet plane. The upper surface 2 and the lower surface 11 of theretainer 1 extend perpendicular to the inner tooth surface 17.

FIG. 6a shows an alternative formed retainer 1″ which has a square crosssection and is mounted in its bonding portion by means of the bondingmaterial 16 at the incisor 14 such that it is completely surrounded bythe bonding material 16.

Finally, FIG. 7 shows a plan view of a nitinol sheet 20, wherein theprocess of working out the retainer 1 according to the invention in FIG.1 has just been completed and the finally cut out retainer 1 is stilldisposed within the nitinol sheet 20. The surface of the nitinol sheet20 and the retainer 1 which extends in the drawing plane corresponds tothe upper nitinol sheet surface 19 or the upper side 2 of the retainer1. The cutting edge 18 of the retainer 1, of which only a line 21 isvisible in the figure, extends perpendicular to the drawing plane. Itcorresponds to the machining surface 13 of the retainer 1, which comesto abut the inner tooth surface 17. A cutting edge 22 extending parallelto the cutting edge 18, which again is only visible as a line 24 in FIG.7, is also to be regarded as a machining surface 23, which faces awayfrom the inner tooth surface 17 in the inserted state.

REFERENCE NUMERALS AND DESIGNATIONS

1, 1′, 1″ retainer

2 upper surface

3 arc

4 formation

5 wave

6, 6′ tip

7 enveloping parabola

8 enveloping parabola

9 front surface

10 rear surface

11 lower surface

12 processing plane

13 machined surface

14 incisor

15 gums

16 bonding material

17 inner tooth surface

18 cutting edge

19 upper metal sheet surface

20 nitinol sheet

21 line

22 cutting edge

23 machined surface

24 line

What is claimed is:
 1. A retainer adapted to cooperate with a pluralityof teeth and configured to stabilize the plurality of teeth, theretainer comprising: at least one elongated arc which is shaped overallto a natural curvature of a lower jaw or an upper jaw, wherein the atleast one elongated arc is locally adapted individually to a surfacecontour of respective abutting teeth, wherein the retainer is machinedfrom a sheet metal plate and includes two mutually parallel surfaces,wherein the sheet metal plate is made from a nickel titanium alloy,wherein the retainer contacts a tooth surface in an installed conditionof the retainer, wherein a machined surface of the retainer faces thetooth surface in the installed condition of the retainer, wherein anupper side or a lower side of the retainer corresponds to an originalsurface plane of the sheet metal plate, and wherein the retainer islocally formed so that it protrudes at least partially into aninterdental space arranged between two adjacent teeth so that a relativemovement between the retainer and the two adjacent teeth directed in alongitudinal direction of the retainer is blocked even when the retainerabuts at the two adjacent teeth in an unconnected state.
 2. The retaineraccording to claim 1, wherein the retainer is able to connect to therespective abutting teeth within bonding portions by a bonding materialin a force-transferring manner, wherein the retainer is embedded in thebonding material and is able to adhere to the respective abutting teeth,wherein a position of the retainer is able to be positioned a minimumdistance from a respective tooth surface measured perpendicular to therespective tooth surface, and wherein a maximum distance between therespective tooth surface and the position of the retainer, is able to beset at the most 0.1 mm in each of the bonding portions.
 3. The retaineraccording to claim 1, wherein the arc has a local radius of curvature of1.0 mm or less.
 4. The retainer according to claim 1, wherein the archas a parallelogram-shaped or rectangular cross section, and whereinside lengths of the cross section are at most 0.7 mm.
 5. The retaineraccording to claim 1, wherein the retainer is able to connect to atleast three teeth in a force-transferring manner.
 6. The retaineraccording to claim 1, wherein the retainer is completely enclosed by abonding material at the bonding portions.
 7. The retainer according toclaim 1, wherein the retainer is configured in one piece.
 8. Theretainer according to claim 1, wherein the retainer viewed in plan viewis enclosable by an inner enveloping parabola and an outer envelopingparabola, and wherein when installed locally in a region of aninterdental space a distance measured perpendicular to the innerenveloping parabola between the inner enveloping parabola and the outerenveloping parabola is at least 1.0 mm.
 9. The retainer according toclaim 1, wherein the retainer has an at least partially roughenedsurface, and wherein all surfaces extending in the longitudinaldirection of the retainer are roughened.
 10. The retainer according toclaim 1, wherein a surface of the retainer is at least partially treatedby electro-polishing or plasma polishing.
 11. The retainer according toclaim 1, wherein the nickel titanium alloy has an AF temperature between25° C. and 35° C.
 12. A method for producing a retainer comprising thesteps: detecting individual contours of teeth to be stabilized andgenerating a detected contour; converting the detected contour of theteeth into a digital model and designing the retainer on the basis ofthe model; machining the designed retainer from a metal sheet which ismade from of a nickel titanium alloy, on the basis of the model using acomputer-controlled process, installing the retainer so that a machinedsurface of the retainer faces a tooth surface at which the retainerabuts, wherein an upper side or a lower side of the retainer correspondsto an original surface plane of the sheet metal, and wherein theretainer is locally formed so that it protrudes at least partially intoan interdental space arranged between two adjacent teeth so that arelative movement between the retainer and the two adjacent teethdirected in a longitudinal direction of the retainer is blocked evenwhen the retainer abuts at the two adjacent teeth in an unconnectedstate.
 13. The method according to claim 12, wherein the retainer is cutout from the metal sheet by laser cutting or by wire erosion.
 14. Themethod according to claim 12, wherein a contour of the teeth to bestabilized is detected intraorally.
 15. The method according to claim12, wherein the metal sheet from which the retainer is machined iscurved about at least one axis of curvature, and wherein the at leastone axis of curvature extends within a surface plane of the metal sheet.16. The method according to claim 12, wherein the retainer after it hasbeen machined from the metal sheet is electro-polished or plasmapolished, so that edges of the retainer are rounded.
 17. A retainer ableto cooperate with a plurality of teeth and configured to stabilize theplurality of teeth, the retainer comprising: at least one elongated arcwhich is shaped overall to a natural curvature of a lower jaw or anupper jaw, wherein the at least one elongated arc is locally adaptedindividually to a surface contour of respective abutting teeth, whereinthe retainer is machined from a sheet metal plate and includes twomutually parallel surfaces, wherein the retainer is able to connect tothe respective abutting teeth within bonding portions by a bondingmaterial in a force-transferring manner, wherein the retainer isembedded in the bonding material and able to adhere to the respectiveabutting teeth, wherein a maximum distance between a respective toothsurface and a position of the retainer is at the most 0.1 mm in each ofthe bonding portions, and wherein the retainer is locally formed so thatit protrudes at least partially into an interdental space arrangedbetween two adjacent teeth so that a relative movement between theretainer and the two adjacent teeth directed in a longitudinal directionof the retainer is blocked even when the retainer abuts at the twoadjacent teeth in an unconnected state.
 18. A method for producing aretainer comprising the steps: detecting individual contours of teeth tobe stabilized and generating a detected contour; converting the detectedcontour of the teeth into a digital model and designing the retainer onthe basis of the model; machining the designed retainer from a metalsheet which is made from of a nickel titanium alloy on the basis of themodel using a computer-controlled process, installing the retainer sothat a machined surface of the retainer faces a tooth surface at whichthe retainer abuts, wherein an upper side or a lower side of theretainer corresponds to an original surface plane of the sheet metal,and wherein the retainer is locally formed so that it protrudes at leastpartially into an interdental space arranged between two adjacent teethso that a relative movement between the retainer and the two adjacentteeth directed in a longitudinal direction of the retainer is blockedeven when the retainer abuts at the two adjacent teeth in an unconnectedstate.
 19. A method for producing a retainer cooperating with aplurality of teeth and configured to stabilize the plurality of teeth,the retainer comprising: at least one elongated arc which is shapedoverall to a natural curvature of a lower jaw or an upper jaw, whereinthe at least one elongated arc is locally adapted individually to asurface contour of respective abutting teeth, and wherein the retaineris machined from a sheet metal plate and includes two mutually parallelsurfaces, the method comprising the steps of: detecting individualcontours of teeth to be stabilized and generating a detected contour;converting the detected contour of the teeth into a digital model anddesigning the retainer on the basis of the model; machining the designedretainer from a metal sheet which is made from of a nickel titaniumalloy, on the basis of the model using a computer-controlled process;and installing the retainer so that a machined surface of the retainerfaces a tooth surface at which the retainer abuts, wherein an upper sideor a lower side of the retainer corresponds to an original surface planeof the sheet metal, and wherein the retainer is locally formed so thatit protrudes at least partially into an interdental space arrangedbetween two adjacent teeth so that a relative movement between theretainer and the two adjacent teeth directed in a longitudinal directionof the retainer is blocked even when the retainer abuts at the twoadjacent teeth in an unconnected state.